Thursday, 12 April 2012

Cellular Mechanisms of Learning

In a comment on a recent post, BusyB asked if I had read the book The Talent Code by Daniel Coyle. I had not at the time, but quickly requested it from the good ol’ Vancouver Public Library. The author has a pretty straightforward premise: to get good at something, you have to engage in what he calls “deep practice”, and this increases your talent by causing the growth of myelin in your brain.

What do I think about this? I’ll talk about talent and practice (and the inevitable nature-vs-nurture question) at a later date, but today I want to talk about what happens in our brain when we learn something. Let me say right off that I find Coyle’s claim that skill-building equals myelin growth such a gross oversimplification that I literally cringed every time myelin was mentioned. The book was peppered with repeated sentences such as “Skill is myelin insulation that wraps neural circuits”. And, really? It’s just not that simple. Sorry.

Let me back up and tell you a little bit about neurons and synapses and myelin and what we think happens to them during learning.

Neurons in a nutshell

You probably know that neurons are brain cells, and you have billions of them in your head and spinal cord. Neurons “talk” to one another electrically through specialized connections called synapses. Here’s a schematic view of two neurons (one blue, the other green) connected by a couple of synapses.

The axon is the part of the neuron that carries electrical impulses away from the cell body. At the end of the axon, there are specialized endings where the electrical signal gets transferred onto the dendrites of another neuron. These are the synapses. In most neurons, the axon is wrapped up in an electrical insulator made of a substance called myelin. Electrical impulses travel faster down axons that are insulated, and so the presence and amount of myelin on an axon alters the neuron's ability to transmit electrical signals.

Learning makes stronger connections between neurons

That’s, in a very small nutshell, how neurons work. And although I’ve only shown two neurons in my diagram, every neuron is connected to many, many other neurons, forming a complex spider’s web of neuronal circuits. Almost everything that happens in our brains comes down to circuits of neurons transmitting electrical signals. So when we learn something new, or get better at doing something, what happens in our brains is that the neuronal circuits responsible for that fact or skill become stronger, better able to communicate with one another.

There are several main ways in which this can happen:

1) The synapses themselves become stronger and so transmit the signals more reliably

2) New synapses form, so the neurons are more strongly connected

3) Myelin growth leads to faster transmission of the electrical signals down the axon, and better timing of neuronal signals.

The synaptic mechanisms (numbers 1 and 2 above) have been studied in excruciating detail (or at least that's how it feels to people like me who have spent years in nitty-gritty synaptic research) and scientists as a group are slowly getting a handle on how changes in synapses happen and how this helps us learn things.

Neurons that fire together wire together

Here’s how scientists think that learning works: The basic idea is that every thought is encoded by the firing of a specific group of neurons, all connected in a circuit. So a particular circuit fires when we think of the note middle C, for example. And there’s another circuit that fires when we picture a note on the first ledger line below the treble clef staff. When we learn that this position on the staff corresponds to middle C, both of these circuits fire at the same time. And when neurons fire at the same time, the connections between the neurons get stronger. The synapses get stronger, and/or new synapses form. This means that the next time we fire the circuit that means “note on the first ledger line below the staff”, the circuit that corresponds to “middle C” is more likely to fire. Neuroscientists have a saying for this: "Neurons that fire together wire together”. From a learning standpoint, it means that we have learned to connect those two ideas by physically altering the way the neurons in our brain are connected.

These changes in synaptic strength very clearly happen when we learn something, whether new facts or new skills. Synaptic changes are an important part of learning during development, and relearning following brain injury. There is a ton of research showing this. The fact that Coyle doesn’t even mention these types of mechanisms as taking place during learning is kind of ridiculous.

Myelin and Learning
So what about myelin? Does myelin growth aid in skill learning, as Coyle purports? The answer, based on scientific research, is “probably”. There are correlational studies showing that people who are more skilled at certain tasks (like reading, or playing music) have greater myelination in areas of the brain related to those tasks. In particular, musicians have a larger and more myelinated corpus callosum, the axon bundle that connects the two halves of the brains. This is especially true for musicians who began their musical training before the age of 7, which makes sense, because the myelination of the nervous system is something that occurs throughout childhood and is not complete until a person is in their mid-twenties. Myelination of neurons during learning in adults is still a controversial idea, and research in this area is on-going. I’m interested in this line of research, especially the thought that the amount of myelin helps to co-ordinate the arrival of signals from different neurons. Perhaps myelination plays a greater role in learning of skills compared to learning of facts (implicit vs. explicit learning), but I was not able to find any evidence for this in the scientific literature.

What do I think about The Talent Code? I agree with the (rather obvious) idea that hard works leads to the acquisition of skills, but I think there are better and more interesting books that address this topic (this one, for example). However, I think the scientific side of his book is weak, oversimplified and kind of misleading.

About Me

Tara Gaertner is a neuroscientist, music educator, writer and speaker. She holds a Bachelor’s degree in Music from McGill University and a Ph.D. in Neuroscience from the University of Texas, Houston. She has taught piano, flute, and music theory since 1988 and currently teaches the Music for Young Children program as well as private piano and flute lessons. She is an Adjunct Professor at the University of British Columbia, lecturing on Neuroscience in the department of Occupational Science and Occupational Therapy.